1. Technical Field
This disclosure relates to an image forming apparatus including a recording head configured to discharge liquid droplets.
2. Description of the Background
One example of related-art image forming apparatuses having two or more of printing, copying, plotting, and facsimile functions includes an inkjet recording device employing a liquid discharge recording method. The inkjet recording device includes a recording head configured to discharge droplets of a recording liquid such as ink to form an image on a recording medium such as a sheet while the sheet is conveyed. It is to be noted that the sheet is not limited to paper but includes any medium, such as an OHP sheet, to which liquid droplets such as ink droplets can be adhered.
Examples of the inkjet recording device include a serial-type image forming apparatus, in which the recording head discharges liquid droplets while moving in a main scanning direction to form an image on the sheet, and a line-type image forming apparatus including a line-type recording head configured to discharge liquid droplets does so without moving to form an image on the sheet.
Image forming apparatuses hereinafter described form an image on a recording medium, such as paper, string, fiber, cloth, lather, metal, plastics, glass, wood, and ceramics by discharging liquid droplets onto the recording medium. In this specification, an image refers to both signifying images such as characters and figures, as well as non-signifying images such as patterns. Further, in this specification, ink includes any liquid, such as a recording liquid and a fixing solution, capable of forming an image on the recording medium.
In any such image forming apparatus that uses ink of whatever kind to print on a recording medium, leaks can be a problem. For example, Published unexamined Japanese Patent Application No. (hereinafter referred to as JP-A-) 2007-136769 discloses a serial-type image forming apparatus employing the liquid discharge recording method in which a sub tank such as a head tank and a buffer tank serving as a smaller-capacity liquid container for supplying the ink to the recording head is provided on a carriage including the recording head, and a larger-capacity main tank such as a main cartridge and an ink cartridge is provided on a main body of the image forming apparatus so that the ink is supplied from the main tank to the sub tank.
However, in the above-described serial-type image forming apparatus including the sub tank serving as an ink supply device, the ink may be inadvertently supplied from the main tank to the sub tank due to scanning movement of the carriage including the recording head and the sub tank when a seal provided by a supply pump configured to supply the ink from the main tank to the sub tank starts to deteriorate.
In general, negative pressure is generated in the sub tank in order to form ink meniscus in nozzles provided on the recording head for discharging ink droplets. However, when the ink is inadvertently supplied from the main tank to the sub tank as described above, the ink leaks out of the nozzles of the recording head due to a loss of the negative pressure in the sub tank.
To solve such a problem, JP-A-2002-316422 discloses an image forming apparatus in which a valve including a sealing unit, and a suction pump, are provided in a supply path between a main tank and a sub tank. The valve opens the supply path while the suction pump is in operation, and closes the supply path while the suction pump is not in operation.
However, a complicated configuration is required to include the valve including the sealing unit capable of completely closing the supply path between the main tank and the sub tank, resulting in higher costs.
Another approach is to improve seal performance of the suction pump so that the supply path can be completely closed while the suction pump, is not in operation. However, such a suction pump is required to have higher accuracy, also resulting in higher costs.
Alternatively, a negative pressure detector configured to constantly detect a state of the negative pressure in the sub tank may be provided in the sub tank so that the negative pressure is returned to a normal state when the negative pressure detector detects that the negative pressure in the sub tank is not in the normal state.
However, the above-described configuration cannot be applied to an image forming apparatus in which the negative pressure detector is not provided in the sub tank and the state of the negative pressure in the sub tank is detected at a predetermined position such as a home position of the carriage. Further, in the image forming apparatus in which the state of the negative pressure in the sub tank is detected at the predetermined position as described above, printing operations need to be stopped in order to detect the state of the negative pressure in the sub tank because the state of the negative pressure in the sub tank cannot be detected during the printing operations, causing a decrease in print speed.